The invention relates to a method for filling at least one cavity of a die for the production of a molding from a melt, in particular a cavity of a die in an injection molding machine, the melt being introduced under pressure out of nozzles through a plurality of cutouts into the cavity, which nozzles are assigned sensors which determine the melt stream in the cavity.
In injection molding or, for example, also in diecasting, the cavity in a die is filled with a melt, in particular consisting of plastic, metal or ceramic. This introduction operation takes place until the cavity is at least almost completely filled, this being followed by a changeover to what is known as the holding pressure phase, in which, above all, a contraction of the material in the cavity is also compensated.
DE 101 12 126 A1 discloses a method for the automatic balancing of the volumetric filling of cavities, in particular in multiple injection molding dies, the temperature profile in the cavities being determined and being equalized for other cavities.
DE 101 16 998 A1 (WO 02/08117A), for example, describes how a cavity is detected automatically with the aid of a die wall temperature sensor at the end of the flow path of a cavity, when the plastic melt reaches this point. At this moment, a signal is sent to the machine control, in order to change over from a speed-regulated injection operation to a pressure-controlled holding pressure operation. This publication also indicates the problems in a single die with multiple tie-up for the production of very large injection moldings with long flow paths, of regulating the flow front of the melt up to volumetric filling with the aid of sensors in the cavity, such that the hot duct nozzles can be controlled according to the programming at each injection point.
Furthermore, from JP 2001 179786 A, a method may be gathered, in which melt is introduced out of the nozzle via a distributor through two injection points into a cavity. This cavity is assigned two pressure sensors in the melt path, the opening and closing of corresponding valves upstream of the injection points being regulated on the basis of the signals from said pressure sensors.
Again, from EP 0 704 290 A, a method for the production of plastic injection moldings may be gathered, in which melt is led to a plurality of injection points via a distributor. From a first injection point, a specific quantity of melt is introduced into the cavity and is distributed as a result of the closing of the mold, until the melt reaches a sensor. Thereafter, a second injection point is opened and, again, part of the melt is introduced into the mold and distributed as a result of the further closing of the mold, until a second sensor is activated.
For large-area or large-volume moldings, such as, for example, bumpers, door battens, fittings or the like, cascade injection molding, as it is referred to, is known. Here, injection or filling is not carried out, as in the conventional injection molding method via a central gate, but sequentially via a plurality of controlled nozzles. That is to say, first, only part of the die cavity is filled by the first nozzle. When the melt reaches the position of the second nozzle, the latter opens and fills a further part of the cavity, etc. The optimization of the nozzle opening takes place, as a rule, empirically, there being no possibility of checking the position of the weld lines, that is to say the local meeting of the various melts. This has a decisive influence on the quality of the parts produced.
In general, it is to be noted that, in these applications, because of the long flow paths, fluctuations in the filling of a cavity have a substantially greater effect than where comparatively small moldings are concerned.
The object on which the present invention is based is to improve the cascade injection molding process appreciably.